Draft documentation for the Path class

Author: theofidry

components/filesystem.rst

@@ -4,7 +4,8 @@
 The Filesystem Component
 ========================
 
-    The Filesystem component provides basic utilities for the filesystem.
+    The Filesystem component provides basic utilities for the filesystem and
+    paths manipulation.
 
 Installation
 ------------
@@ -18,16 +19,23 @@ Installation
 Usage
 -----
 
-The :class:`Symfony\\Component\\Filesystem\\Filesystem` class is the unique
-endpoint for filesystem operations::
+The component contains two classes:
+
+- The :class:`Symfony\\Component\\Filesystem\\Filesystem` which provides utilities
+  for filesystem write operations.
+- The :class:`Symfony\\Component\\Filesystem\\Path` which provides utilities
+  for paths manipulation.::
 
     use Symfony\Component\Filesystem\Exception\IOExceptionInterface;
     use Symfony\Component\Filesystem\Filesystem;
+    use Symfony\Component\Filesystem\Path;
 
     $filesystem = new Filesystem();
 
     try {
-        $filesystem->mkdir(sys_get_temp_dir().'/'.random_int(0, 1000));
+        $filesystem->mkdir(
+            Path::normalize(sys_get_temp_dir().'/'.random_int(0, 1000)),
+        );
     } catch (IOExceptionInterface $exception) {
         echo "An error occurred while creating your directory at ".$exception->getPath();
     }
@@ -44,6 +52,9 @@ endpoint for filesystem operations::
     string, an array or any object implementing :phpclass:`Traversable` as
     the target argument.
 
+Filesystem
+----------
+
 ``mkdir``
 ~~~~~~~~~
 
@@ -236,6 +247,11 @@ Its behavior is the following::
     * if ``$path`` does not exist, it returns null.
     * if ``$path`` exists, it returns its absolute fully resolved final version.
 
+.. note::
+
+    If you wish to canonicalize the path without checking its existence, you can
+    use :method:`Symfony\\Component\\Filesystem\\Path::canonicalize` instead.
+
 ``makePathRelative``
 ~~~~~~~~~~~~~~~~~~~~
 
@@ -315,6 +331,191 @@ contents at the end of some file::
 If either the file or its containing directory doesn't exist, this method
 creates them before appending the contents.
 
+Path
+----
+
+.. versionadded:: 5.4
+
+    The :class:`Symfony\\Component\\Filesystem\\Path` class was introduced in Symfony 5.4.
+
+Dealing with file paths usually involves some difficulties:
+
+- System Heterogeneity: file paths look different on different platforms. UNIX
+  file paths start with a slash ("/"), while Windows file paths start with a
+  system drive ("C:"). UNIX uses forward slashes, while Windows uses backslashes
+  by default ("").
+- Absolute/relative paths: web applications frequently need to deal with absolute
+  and relative paths. Converting one to the other properly is tricky and
+  repetitive.
+
+:class:`Symfony\\Component\\Filesystem\\Path` provides utility methods to tackle
+those issues.
+
+Canonicalization
+~~~~~~~~~~~~~~~~
+
+*Canonicalization* is the transformation of a path into a normalized (the
+"canonical") format. You can canonicalize a path with :method:`Symfony\\Component\\Filesystem\\Path::canonicalize`::
+
+    echo Path::canonicalize('/var/www/vhost/webmozart/../config.ini');
+    // => /var/www/vhost/config.ini
+
+The following modifications happen during canonicalization:
+
+- "." segments are removed;
+- ".." segments are resolved;
+- backslashes ("\") are converted into forward slashes ("/");
+- root paths ("/" and "C:/") always terminate with a slash;
+- non-root paths never terminate with a slash;
+- schemes (such as "phar://") are kept;
+- replace "~" with the user's home directory.
+
+You can pass absolute paths and relative paths to :method:`Symfony\\Component\\Filesystem\\Path::canonicalize`.
+When a relative path is passed, ".." segments at the beginning of the path are
+kept::
+
+    echo Path::canonicalize('../uploads/../config/config.yml');
+    // => ../config/config.yml
+
+Malformed paths are returned unchanged::
+
+    echo Path::canonicalize('C:Programs/PHP/php.ini');
+    // => C:Programs/PHP/php.ini
+
+Converting Absolute/Relative Paths
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Absolute/relative paths can be converted with the methods
+:method:`Symfony\\Component\\Filesystem\\Path::makeAbsolute`
+and :method:`Symfony\\Component\\Filesystem\\Path::makeRelative`.
+
+:method:`Symfony\\Component\\Filesystem\\Path::makeAbsolute` expects a relative
+path and a base path to base that relative path upon::
+
+    echo Path::makeAbsolute('config/config.yml', '/var/www/project');
+    // => /var/www/project/config/config.yml
+
+If an absolute path is passed in the first argument, the absolute path is
+returned unchanged::
+
+    echo Path::makeAbsolute('/usr/share/lib/config.ini', '/var/www/project');
+    // => /usr/share/lib/config.ini
+
+The method resolves ".." segments, if there are any::
+
+    echo Path::makeAbsolute('../config/config.yml', '/var/www/project/uploads');
+    // => /var/www/project/config/config.yml
+
+This method is very useful if you want to be able to accept relative paths (for
+example, relative to the root directory of your project) and absolute paths at
+the same time.
+
+:method:`Symfony\\Component\\Filesystem\\Path::makeRelative` is the inverse
+operation to :method:`Symfony\\Component\\Filesystem\\Path::makeAbsolute`::
+
+    echo Path::makeRelative('/var/www/project/config/config.yml', '/var/www/project');
+    // => config/config.yml
+
+If the path is not within the base path, the method will prepend ".." segments
+as necessary::
+
+    echo Path::makeRelative('/var/www/project/config/config.yml', '/var/www/project/uploads');
+    // => ../config/config.yml
+
+Use :method:`Symfony\\Component\\Filesystem\\Path::makeAbsolute` and
+:method:`Symfony\\Component\\Filesystem\\Path::makeRelative` to check whether a
+path is absolute or relative::
+
+    Path::isAbsolute('C:\Programs\PHP\php.ini')
+    // => true
+
+All four methods internally canonicalize the passed path.
+
+Finding Longest Common Base Paths
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When you store absolute file paths on the file system, this leads to a lot of
+duplicated information::
+
+    return array(
+        '/var/www/vhosts/project/httpdocs/config/config.yml',
+        '/var/www/vhosts/project/httpdocs/config/routing.yml',
+        '/var/www/vhosts/project/httpdocs/config/services.yml',
+        '/var/www/vhosts/project/httpdocs/images/banana.gif',
+        '/var/www/vhosts/project/httpdocs/uploads/images/nicer-banana.gif',
+    );
+
+Especially when storing many paths, the amount of duplicated information is
+noticeable. You can use :method:`Symfony\\Component\\Filesystem\\Path::getLongestCommonBasePath`
+to check a list of paths for a common base path::
+
+    $paths = array(
+        '/var/www/vhosts/project/httpdocs/config/config.yml',
+        '/var/www/vhosts/project/httpdocs/config/routing.yml',
+        '/var/www/vhosts/project/httpdocs/config/services.yml',
+        '/var/www/vhosts/project/httpdocs/images/banana.gif',
+        '/var/www/vhosts/project/httpdocs/uploads/images/nicer-banana.gif',
+    );
+
+    Path::getLongestCommonBasePath($paths);
+    // => /var/www/vhosts/project/httpdocs
+
+Use this path together with :method:`Symfony\\Component\\Filesystem\\Path::makeRelative`
+to shorten the stored paths::
+
+    $bp = '/var/www/vhosts/project/httpdocs';
+
+    return array(
+        $bp.'/config/config.yml',
+        $bp.'/config/routing.yml',
+        $bp.'/config/services.yml',
+        $bp.'/images/banana.gif',
+        $bp.'/uploads/images/nicer-banana.gif',
+    );
+
+:method:`Symfony\\Component\\Filesystem\\Path::getLongestCommonBasePath` always
+returns canonical paths.
+
+Use :method:`Symfony\\Component\\Filesystem\\Path::isBasePath` to test whether a
+path is a base path of another path::
+
+    Path::isBasePath("/var/www", "/var/www/project");
+    // => true
+
+    Path::isBasePath("/var/www", "/var/www/project/..");
+    // => true
+
+    Path::isBasePath("/var/www", "/var/www/project/../..");
+    // => false
+
+Finding Directories/Root Directories
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+PHP offers the function :phpfunction:`dirname` to obtain the directory path of a
+file path. This method has a few quirks::
+
+- `dirname()` does not accept backslashes on UNIX
+- `dirname("C:/Programs")` returns "C:", not "C:/"
+- `dirname("C:/")` returns ".", not "C:/"
+- `dirname("C:")` returns ".", not "C:/"
+- `dirname("Programs")` returns ".", not ""
+- `dirname()` does not canonicalize the result
+
+:method:`Symfony\\Component\\Filesystem\\Path::getDirectory` fixes these
+shortcomings::
+
+    echo Path::getDirectory("C:\Programs");
+    // => C:/
+
+Additionally, you can use :method:`Symfony\\Component\\Filesystem\\Path::getRoot`
+to obtain the root of a path::
+
+    echo Path::getRoot("/etc/apache2/sites-available");
+    // => /
+
+    echo Path::getRoot("C:\Programs\Apache\Config");
+    // => C:/
+
 Error Handling
 --------------